1. Field of the Invention
This invention relates to a sheet transport device for use in an image forming apparatus such as a copier, a facsimile machine, a printer, and a scanner to transport recording paper, documents, and the like.
2. Description of the Related Art
There are known sheet transport devices equipped with a plurality of sheet transport paths. Recently, copiers incorporated with a plurality of sheet cassettes have been widespread. Such a copier is generally equipped with a plurality of sheet transport paths.
FIG. 15 is a perspective view of a copier incorporated with a plurality of sheet cassettes arranged at respective positions, specifically showing a state that a side door of the copier is opened. FIGS. 16A and 16B are enlarged sectional views illustrating a conventional sheet transporting section of a copier. FIG. 16A shows a state that a side door of the copier is closed, and FIG. 16B shows a state that the side door is opened.
The aforementioned copier is equipped with a group of sheet cassettes 111 consisting of, for example, four sheet cassettes 111a, 111b, 111c, and 111d each accommodating a stack of sheets therein. The copier is constructed in such a manner that a copy sheet 115 is dispensed from an arbitrary sheet cassette of the sheet cassette group 111, fed to an image forming section via a specified sheet transport path, has an image formed and fixed thereon, and is discharged onto a discharge tray.
The sheet transporting section is adapted to transport a sheet 115 dispensed from any one of the sheet cassettes 111a to 111d to the image forming section located at an upper part of the copier along a specified transport path from upstream toward downstream with respect to a sheet transport direction.
Specifically, as shown in FIGS. 16A and 16B, each sheet cassette has the following configuration. For example, the uppermost sheet cassette 111a has a first sheet transport path 211 along which a sheet 115 dispensed therefrom is transported toward the image forming section, and a second sheet transport path 212 along which a sheet 115 dispensed from a lower-side sheet cassette (e.g., sheet cassette 111b) is transported toward the image forming section. The first sheet transport path 211 and the second sheet transport path 212 are jointed at an upper part of the sheet cassette and directed upward. Likewise, the sheet cassette located below the sheet cassette 111a (for example, sheet cassette 111b) has a sheet transport path (namely, a first sheet transport path 211) dedicatedly used for the sheet cassette 111b, and a sheet transport path (namely, a second sheet transport path 212) which extends from a lower-side sheet cassette and is jointed at an upper part of the sheet cassette 111b (see the upper part of each sheet cassette in FIGS. 16A and 16B).
A guide member 220 for switching over a sheet transport path between the first sheet transport path 211 and the second sheet transport path 212 is provided at each jointed part of the first sheet transport path 211 and the second sheet transport path 212. When a side door 230 is opened in the direction shown by the arrow A in FIG. 16B, the guide member 220 is changeable to an opened position by pivotal rotation thereof indicated by the arrow B in FIG. 16B, whereby the interior of the first sheet transport path 211 is exposed. When the guide member 220 is set to the opened position, an operator can remove a sheet jammed or staying in the first sheet transport path 211. Likewise, the second sheet transport path 212 is exposed outside when the side door 230 is opened, whereby an operator can remove a jammed sheet from the second sheet transport path 212.
Changing over the guide member 220 between the opened position (position for exposing the interior of the first sheet transport path 211) and the closed position (position for defining the first sheet transport path 211 of a certain configuration) is associated with opening and closing of the side door 230. Closing the side door 230 pivotally rotates the guide member 220 to the closed position by pressing a lead end of the guide member 220 against an inner wall of the side door 230 (see FIG. 16A). Opening the side door 230 releases pressing of the guide member 220 to thereby allow the guide member 220 to pivotally set to the opened position (see FIG. 16B).
The copier shown in FIGS. 15 to 16B is operated in such a manner that the side door 230 is pivotally openable about a vertical axis. Hereafter, this type of copier is also referred to as xe2x80x9csideways openable copierxe2x80x9d. In the case of a copier operated in such a manner that a side At door is pivotally openable about a horizontal axis (hereafter, also referred to as xe2x80x9cvertically openable copierxe2x80x9d), similar to the sideways openable copier, an operation of a guide member for switching over a sheet transport path between a first sheet transport path and a second sheet transport path is associated with opening and closing of the side door. Pressing a lead end of the guide member against the inner wall of the side door pivotally sets the guide member to the closed position. FIG. 17 is a sectional view of a vertically openable copier specifically showing a state that a side door 230 is opened.
It is preferable to provide a guide member 220 having a relatively large size in order to set an opening angle of the guide member 220 with respect to a vertical plane as large as possible to sufficiently expose the interior of the first sheet transport path 211 in light of an operator""s operability of removing a jammed sheet from the first sheet transport path 211 (see FIGS. 16A and 16B). However, the aforementioned conventional copier (specifically, sheet transport device) involves the following drawback.
Specifically, as shown in FIG. 18, which is a perspective view for illustrating open/close operations of the guide member 220 in association with open/close operations of the side door 230, pressing the guide member 220 by the side door 230 as the side door 230 is being closed enables to set the guide member 220 to the closed position. With this arrangement, it is likely that part on the inner surface of the side door 230 abutted against the guide member 220 (part indicated by the arrow C in FIG. 18A) is subjected to an abrasion or frictional resistance. Particularly, in the case where the guide member 220 is set at a large opening angle, the abutted part (region around the arrow C in FIG. 18) of the side door 230 and the guide member 220 is subjected to a high abrasion or frictional resistance. As shown in FIG. 18B, closing motion of the side door 230 about an axis V cannot be smoothly transferred to a rotational motion of the guide member 220 around an axis H because the closing motion of the side door 230 does not create a force, i.e., a upwardly acting force component to produce a moment MH, required to rotate the guide member 220 upward. Therefore, it is highly likely that the abutted part on the side door 230 and the guide member 220 are damaged or lost.
In the case of a vertically openable copier, although a physical load exerted to part of a side door and a guide member corresponding to the aforementioned abutted part is small compared to the case of a sideways openable copier, the part of the side door 230 and the guide member 220 is subjected to a physical load if the guide member 220 is attempted to be set at a large opening angle.
In view of the aforementioned drawbacks, in the conventional sheet transport device, a maximal openable angle of the guide member 220 is restricted, thus hindering operability in removing a jammed sheet.
In view of the above, it is an object of the invention to provide a sheet transport device free from the problems residing in the prior art.
It is a further object of the invention to provide a sheet transport device capable of setting an opening angle of a guide member as large as possible.
According to an aspect of this invention, a sheet transport device for use in an image forming apparatus, comprises: a guide member, which is pivotally supported on a main body of the image forming apparatus to be movable between a closed position and an opened position; a first counterpart member having a surface, which with one surface of the guide member, when in the closed position, forms a first sheet transport path; a second counterpart member which is pivotally supported on the main body of the image forming apparatus to be movable between a closed position and an opened position, said second counterpart member in the closed position forms a second sheet transport path with the opposite surface of the guide member in the closed position and said second counterpart member in the opened position exposes the interior of the second sheet transport path; and retaining means for retaining the guide member at the closed position when the second counterpart member is in the open position.
With this arrangement, an operator can remove a jammed sheet by setting the second counterpart member to the opened position and exposing the interior of the second sheet transport path. Also, the operator can remove a jammed sheet by setting the guide member to the opened position and exposing the interior of the first sheet transport path. Since the guide member is operable independently of opening/closing of the second counterpart member, and the retaining means retains the guide member at the closed position, the sheet transport device is free from a problem of loss and damage of part of the guide member and the second counterpart member (e.g., a side door) due to abrasion or frictional resistance as having been encountered in the conventional arrangement. Further, since guide member is operated independently of opening/closing of the second counterpart member, there is no limit to an opening angle of the guide member. For instance, the opening angle of the guide member may be set at 90xc2x0 or larger. Setting the opening angle as wide as 90xc2x0 or larger improves operability in removing a jammed sheet.
These and other objects, features and advantages of the present invention will become more apparent upon a reading of the following detailed description and accompanying drawing.